Ch.9 Muscles and Muscle Tissue

Thick and thin filaments (myofilaments in a sarcomere)

Central thick filaments containing myosin extend the entire length of the A band; connected in the middle of the sarcomere at the M line Lateral thin filaments containing actin (blue) extend across the I band and partway into the A band; Z disc, a protein sheet, anchors the thin filaments

What is the difference between a tendon and a ligament?

A tendon attaches muscles to bones, whereas a ligament connects bones at joints.

What is a skeletal muscle fiber? What do they contain?

(Huge cells) Long cylindrical cell with multiple oval nuclei just beneath its sarcolemma or plasma membrane Hundreds of embryonic cells fuse to produce each fiber Contain calcium-regulated molecular motors

Explain the structure of thick filaments

Thick filaments are composed primarily of the protein myosin Each myosin molecule consists of six polypeptide chains: two heavy (high-molecular-weight) chains and four light chains Heavy chains twist together to form myosin's rodlike tail, and each heavy chain ends in a globular head that is attached to the tail via a flexible hinge

Explain the structure of thin filaments

Thin filaments are composed chiefly of the protein actin - Actin has kidney-shaped polypeptide subunits, called globular actin or G actin. - Each G actin has a myosin-binding site (or active site) to which the myosin heads attach during contraction - Polypeptide strands of tropomyosin, a rod-shaped protein, spiral about the actin core and help stiffen and stabilize it - Troponin, the other major protein in thin filaments, is a globular protein with three polypeptide subunits

DMD is caused by what

DMD is caused by a defective gene for dystrophin - Dystrophin links the cytoskeleton to the extracellular matrix and, like a girder, helps stabilize the sarcolemma -

What are the 2 types of muscle attachments?

Direct or fleshy attachments- the epimysium of the muscle is fused to the periosteum of a bone or perichondrium of a cartilage Indirect attachments- the muscle's connective tissue wrappings extend beyond the muscle either as a ropelike tendon or as a sheetlike aponeurosis - Tendon or aponeurosis anchors the muscle to the connective tissue covering of a skeletal element (bone or cartilage) or to the fascia of other muscles.

What are the 3 types of muscle sheaths and what are they made up of?

Epimysium- "overcoat" of dense irregular connective tissue that surrounds the whole muscle Perimysium- Surrounding each fascicle is a layer of dense irregular connective tissue called perimysium Endomysium- wispy sheath of connective tissue that surrounds each individual muscle fiber. It consists of fine areolar connective tissue. All of these connective tissue sheaths are continuous with one another as well as with the tendons that join muscles to bones

What are characteristics of muscle tissue?

Excitability- responsiveness, is the ability of a cell to receive and respond to a stimulus by changing its membrane potential. In the case of muscle, the stimulus is usually a chemical—for example, a neurotransmitter released by a nerve cell. Contractility- ability to shorten forcibly when adequately stimulated. This ability sets muscle apart from all other tissue types. Extensibility- ability to extend or stretch. Muscle cells shorten when contracting, but they can be stretched, even beyond their resting length, when relaxed. Elasticity- ability of a muscle cell to recoil and resume its resting length after stretching.

Muscular dystrophy

Group of inherited muscle-destroying diseases that generally appear during childhood -Affected muscles initially enlarge due to deposits of fat and connective tissue, but the muscle fibers atrophy and degenerate

Name the types of bands and lines in a myofibril

I band- contains only thin filaments Z disc- it is the midline in the I band; darker area A band- contains BOTH thick and thin filaments H zone- thick filaments only; bisected vertically by a dark line called the M line (M for middle) formed by molecules of the protein myomesin M line- area where thick filaments are linked by accessory proteins

What happens when a muscle contracts (origin and insertion)

When a muscle contracts, the movable bone, the muscle's insertion, moves toward the immovable or less movable bone, the muscle's origin In the muscles of the limbs, the origin typically lies proximal to the insertion

Dystrophin

Links the thin filaments to the integral proteins of the sarcolemma

Why are connective tissue sheaths important?

- Together these sheaths support each cell and reinforce and hold together the muscle, preventing the bulging muscles from bursting during exceptionally strong contractions. - All of these connective tissue sheaths are continuous with one another as well as with the tendons that join muscles to bones - When muscle fibers contract, they pull on these sheaths, which transmit the pulling force to the bone to be moved.

Explain the structure of muscles in terms of sheaths and what they cover

1) The epimysium (dense irregular connective tissue that surrounds the whole muscle) The muscle is composed of many fascicles. 2) Surrounding each fascicle is a layer of dense irregular connective tissue called perimysium) and one fascicle is composed of many muscle fibers 3) The endomysium (fine areolar connective tissue) wraps between individual muscle fibers 4) Each muscle fiber is composed of many myrofibrils (single muscle fiber contains hundreds to thousands of rodlike myofibrils that run parallel to its length) 5) Myofibrils are made up of a chain of sarcomeres linked end to end 6) Sarcomeres contain even smaller rodlike structures called myofilaments (region of a myofibril between two successive Z discs) - smallest contractile unit of a muscle fiber—the functional unit of skeletal muscle 7) These smaller structures, the myofilaments or filaments, are the muscle equivalents of the actin-containing microfilaments and myosin motor proteins

Elastic filaments

Composed of the giant protein titin - Titin: holds the thick filaments in place, maintaining the organization of the A band, and helps the muscle cell spring back into shape after stretching - Titin does not resist stretching in the ordinary range of extension, but it stiffens as it uncoils, helping the muscle resist excessive stretching

What type of muscle attachments are more common?

Indirect attachments are much more common because of their durability and small size - Tendons are mostly tough collagen fibers, which can withstand the abrasion of rough bony projections that would tear apart the more delicate muscle tissues - B/c of their relatively small size, more tendons than fleshy muscles can pass over a joint—so tendons also conserve space

Duchenne muscular dystrophy (DMD)

Most common and serious form of muscular dystrophy: inherited as a sex-linked recessive disease - Expressed almost exclusively in males; diagnosed in boys between 2 and 7 years old - Normal-appearing boys become clumsy and fall frequently as their skeletal muscles weaken - Disease progresses relentlessly from the extremities upward, finally affecting the head and chest muscles, and cardiac muscle Treatment: weakness continues to progress, but with supportive care, DMD patients are living into their 30s and beyond

What are the four general functions of muscles?

Produce movement- Skeletal muscles are responsible for all locomotion and manipulation. They enable you to respond quickly to jump out of the way of a car, direct your eyes, and smile or frown. Maintain posture and body position- muscles function almost continuously, making one tiny adjustment after another to counteract the never-ending downward pull of gravity. Stabilize joints- Even as they pull on bones to cause movement, they strengthen and stabilize the joints of the skeleton. Generate heat- Muscles generate heat as they contract, which plays a role in maintaining normal body temperature.

What is the sarcoplasm? What does the sarcoplasm contain?

Sarcoplasm- cytoplasm of a muscle cell, is similar to the cytoplasm of other cells Contains unusually large amounts of glycosomes (granules of stored glycogen that provide glucose during muscle cell activity for ATP production) and myoglobin, a red pigment that stores oxygen

Why is it important that skeletal muscle have a rich blood supply?

Skeletal muscle has a rich blood supply --> contracting muscle fibers use huge amounts of energy and require almost continuous delivery of oxygen and nutrients via the arteries. Muscle cells also give off large amounts of metabolic wastes that must be removed through veins if contraction is to remain efficient.

What is skeletal muscle made up of?

Skeletal muscle is made up of muscle fibers, nerves, blood vessels, and connective tissues